THE NEW INOCULATION.
Any account of the scientific progress of this century which omits the name of Louis Pasteur would be lamentably incomplete. In that part of science which relates strictly to human life and the means of preserving it, the work of this great man must be placed in the first rank. Indeed, we believe that no other stride in biological investigation from the beginning of time has been so great in its immediate and prospective results as has been the increment contributed by Pasteur and his contemporary Koch. The success of these two experimental philosophers grew out of the substitution of a new theory for one that had hitherto prevailed respecting some of the fundamental processes in living matter.
Up to about the close of the third quarter of this century, the belief continued to prevail in the possibility of the propagation and production of germ life without other germ life to precede it. It was held that fermentation is not dependent upon living organisms, and that fermentation may be excited in substances from which all living germs have been excluded. This belief led to the theory of abiogenesis so-called—a term signifying the production of life without life to begin with.
The question involved in this theory was hotly debated by philosophers and scientists in the Sixties and Seventies. The first great work of Pasteur in biological investigation was his successful demonstration of the impossibility of spontaneous generation. About 1870, he became a careful experimenter with the phenomena of fermentation. As his work proceeded, he was more convinced that fermentation can never occur in the absence and exclusion of living germs; and this view of the deep-down processes in living matter has now been accepted as correct.
The next stage in the work of Pasteur was the discovery that certain substances, such as glycerine, are products of fermentation. From this foundation firmly established he passed on to consider the phenomena of disease. He had been, in the first place, a teacher in a normal school at Paris. In 1863, when he was thirty-nine years of age, he was a professor of geology. Afterward he had a chair of chemistry at the Sorbonne. In 1856 we find him experimenting with light, and after that he turned to biological investigations. This led him to the results mentioned above, and presently to the discovery that the contagious and infectious diseases with which men and the lower animals are affected are in general the results of processes in the system that are nearly analagous to fermentation, and that such diseases are therefore traceable ultimately to the existence of living germs.
This view of the case brought Pasteur to a large and general investigation of bacteria. The bacterium may be defined as a microscopic vegetable organism; or it may be called an animal organism; for in the deep-down life of germs there is not much difference between vegetable and animal—perhaps no difference at all. The bacterium is generally a jointed rod-like filament of living matter, and its native world seems to be any putrefying organic substance.
Bacteria are the smallest of microscopic organisms. They are widely diffused in the natural world, existing independently and also in a parasitical way, in connection with larger forms of organic life. They multiply with the greatest rapidity. On the whole, the bacterium fulfills its vital offices in two ways, or with two results; first, fermentation, and secondly, disease.
To this field of inquiry Pasteur devoted himself with the greatest assiduity. He began to investigate the diseased tissue of animals, and was rewarded with the discovery of the germs from which the disease had come. It was found that the bacteria of one disease are different from those of another disease, or in a word that the microscopic organisms which produce morbid conditions in animals are differentiated into genera and species and varieties, in the same manner as are the animals, birds and fishes, of the world. A new realm of life invisible save by the aid of the microscope, began to be explored, and practical results began to follow.
Pasteur at length announced his ability to produce infectious diseases by inoculation; and of this his proofs and demonstrations, were complete. In the next place he announced his ability to counteract the ravages, of certain classes of diseases (those called zymotic) by inoculating the animal suffering therefrom with what he called an "attenuated" or "domesticated" virus of the given disease.
The matter first came to a practical issue by the inoculation of well animals with the attenuated virus. The animals so treated became immune; that is, exempt from the infection of the given disease. Pasteur gave public demonstrations in the fields near Paris, using the disease called splenic fever, and sheep as the subjects of his experimentation. The whole civilized world was astonished with the results. The tests were conducted in such a way as to preclude the possibility of error. It was shown, in a word, that by the simple process of inoculating well animals with the modified poison the infectious disease might be avoided.
It were long to tell the story of the experimentation and discovery that now followed. The last quarter of the century has been fruitful in the greatest results. The bacilli of one disease after another have been discovered, and the means have been invented of defending the larger animal life from the ravages of microscopic organisms.
But what is an "attenuated" virus? Pasteur and other scientists have shown that by the inoculation of suitable material, such as a piece of flesh, with the poison of a given disease, the bacteria on which that disease depends rapidly multiply and diffuse themselves through the substance. If poison be taken from the first body of infected material and carried to another, that other becomes infected; and from that the third; from the third the fourth, and so on to the tenth generation.
It was noticed, however, that with each transference of the virus to a new organic body the bacilli were modified somewhat in form and activity. They became, so to speak, less savage. The bacterium which at the beginning had been for its savagery a wolf, became in the second body a cur; then a hound; then a spaniel; and then a diminutive lapdog! The bacteria were thus said to be "domesticated;" for the process was similar to the domestication of wild animals into tame. The virus was said to be "attenuated;" that is, made thin or fine; that is, its poisonous and death-dealing quality, was so reduced as to make it comparatively innocuous.
If after the process of attenuation was complete—if after the bacteria were once thoroughly domesticated and the poison produced by them be then introduced into a well subject, that subject would indeed become diseased, but so mildly diseased as scarcely to be diseased at all. In such a case the result was of a kind to be called in popular language a mere "touch" of the disease. In such case the severe ravages of the malady would be prevented; but the subject would be rendered incapable of taking the disease a second time.
On this line of fact and theory Pasteur successfully pressed his work. One disease after another was investigated. It was demonstrated in the case of both the lower animals and men that a large number of maladies and plagues might be completely disarmed of their terrors by the process of inoculation. The name of Pasteur became more and more famous. The celebrated Pasteur Institute was founded at Paris, under the patronage of the French Government, and in some sense under the patronage of the whole world. To this establishment diseased subjects were taken for treatment, and here experimentation was carried on over a wide range of facts.
The value of the results attained can hardly be overestimated. The fear which mankind have long entertained on account of plagues and epidemics, and the loss which the animal industries of the world have sustained, were largely abated. As yet the use of the Pasteur methods for the prevention and cure of disease is by no means universal; but the knowledge which has come of his investigations and of the results of them has diffused itself among all civilized nations, and the hygienic condition of almost every community has been most favorably affected by the new knowledge which we possess of bacteria and of the means of destroying them.
Pasteur, whose recent death has been mourned by the best part of mankind, was an explorer and forerunner. His industry in his chosen field of investigation was prodigious. When he was already nearly seventy years of age, he undertook the investigation of hydrophobia, with the purpose of discovering, if he might, the germ of that dreaded disease, thus preparing a method for inoculation against it.
Hydrophobia is one of the most subtle diseases ever known. So obscure and uncertain are its phenomena that many able men have been led to doubt the existence of such a disease! The mythological origin of the malady in the supposed influence of a dog-star seemed to strengthen the view that hydrophobia, as a specific disease, does not exist. It is undeniably true that the great majority of the cases of so-called rabies are pure myths. Under investigation they melt away into nothing but alarm and fiction. However, there appeared to be a residue of actual hydrophobia, though the disease as tested by its name exists in fancy rather than fact.
In any event, Pasteur began to investigate hydrophobia, and at length discovered the bacilli which produce it. At least he found in animals affected with rabies, notably in the spinal marrow of such animals, minute living organisms, having the form of thread-like animalculæ, with heads at one end. The microscope showed also among these thread-like bodies other organisms that were like small circular black specks, or disks.
The next step in the work was to test the result by inoculating a well animal with these bodies. Pasteur selected rabbits for his experimentation. When the experiment was made, the inoculated rabbit was presently attacked with the disease, and soon died in spasms. The repetition of the experiment was attended with like results.
The philosopher next tried his established method of domesticating, or attenuating, the poison. The spinal cord of a rabid dog was obtained, and with this the first rabbit was inoculated. In about two weeks it took hydrophobia. Hereupon the spinal cord was extracted, and the second rabbit was inoculated; then the third; then the fourth, and so on. It was observed, however, that at each stage the intensity of the disease was in this way strangely increased; but the period of inoculation became shorter and shorter.
It was next found that by preserving the spinal cords of the animals that had died of the disease—by preserving them in dry tubes—the poison gradually lost its power. At last the virus seemed to die altogether. Then the experiment of inoculating against the disease was begun. A dog was first inoculated with dead virus. No result followed. Then he was inoculated with stale virus, and then with other virus not so stale. It was found that by continuing this process the animal might be rendered wholly insusceptible to the disease.
The next step was the human stage of experimentation. It was in July of 1885 that Pasteur first employed his method on a human subject. A boy had been bitten and lacerated by a rabid dog. The inoculation was thought to prove successful. Soon afterward some bitten children were taken from the United States to Paris, and were treated against the expected appearance of hydrophobia. Others came from different parts of the continent. Within fourteen months more than two thousand five hundred subjects were treated, and it is claimed that the mortality from hydrophobia was reduced to a small per cent of what it had been before.
It should be said, however, that neither have the results arrived at by Pasteur respecting the character of rabies been so clear, nor have his experiments on subjects supposed to be poisoned with the disease been so successful as in the case of other maladies. It remains, nevertheless, to award to Louis Pasteur the first rank among the bacteriologists of our day, as well as a first place among the philanthropists of the century. Only Robert Koch, of Germany, is to be classed in the same list with him.